DESCRIPTION (Taken from the Investigator's Abstract) The long term, goal of this research is to elucidate the cause(s) of Parkinson's Disease (PD) with a focus on environmental determinants. The investigators propose to investigate the relationship between PD and exposure to pesticides and other factors by conducting a nested case-control study in the Agricultural Health Study (AHS), using a 3:1 case-control ratio and employing classical methods for multi-variate analysis. There are 2 primary aims. Aim 1 will test the hypothesis that pesticide exposure increases PD risk using self-report (life history) and direct (blood, dust) measurements. Aim 2 will test the hypothesis that other (nonpesticide) chemical exposure increases PD risk, using a job-task-based occupational history, and blood testing. Three secondary aims: 1) will test the hypothesis that the soil pathogen Nocardia asteroides causes PD using a battery of assays in blood, soil and dust (aim 3); 2) will assess the role of specific lifestyle and health factors previously reported to alter PD risk (aim 4); and, 3) will assess the effect of specific polymorphisms of xenobiotic metabolizing, genes previously associated with PD on disease risk (aim 5). The studies proposed take full advantage of the AHS, a unique, prospectively studied cohort. The investigators believe that this work could provide a critical and dramatic next step in furthering our knowledge of environmental determinants of PD, and thereby take us closer to our goal of finding its cause(s).